Embedded stress absorber in package

ABSTRACT

A method includes bonding a first package component over a second package component. The second package component includes a plurality of dielectric layers, and a plurality of redistribution lines in the plurality of dielectric layers. The method further includes dispensing a stress absorber on the second package component, curing the stress absorber, and forming an encapsulant on the second package component and the stress absorber.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of the following provisionally filedU.S. Patent application: Application No. 63/085,222, filed on Sep. 30,2020, and entitled “Embedded Corner Damper in Organic Interposer,” whichapplication is hereby incorporated herein by reference.

BACKGROUND

The formation of integrated circuits includes forming integrated circuitdevices on semiconductor wafers, and then sawing the semiconductorwafers into device dies. The device dies may be bonded to packagecomponents such as interposers, package substrates, printed circuitboards, or the like. To protect the device dies and the bondingstructures that bond a device die to a package component, an encapsulantsuch as a molding compound, an underfill, or the like, may be used toencapsulate the device dies.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1-9, 10A, 10B, 10C, 11, 12, 13A, and 13B illustrate thecross-sectional views and top views of intermediate stages in theformation of a package including stress absorbers in accordance withsome embodiments.

FIGS. 14A and 14B illustrate a top view and a cross-sectional view,respectively, of a package including stress absorbers in accordance withsome embodiments.

FIGS. 15 and 16 illustrate the top views of stress absorbers inaccordance with some embodiments.

FIG. 17 illustrates an example amplified view of a part of a stressabsorber and an encapsulant in accordance with some embodiments.

FIG. 18 illustrates a process flow for forming a package in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,”“lower,” “overlying,” “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

A package with stress absorbers therein and the method of forming thesame are provided. In accordance with some embodiments of the presentdisclosure, a device die is bonded to an underlying package componentsuch as an organic interposer. The device die is molded in anencapsulant such as a molding compound. Stress absorbers are also moldedin the encapsulant, and are located close to the corners of theresulting package. The stress absorbers may have a Young's modulus lowerthan the Young's modulus of the encapsulant, so that it may absorb thestress generated due to the difference between the device die and theunderlying package components. Embodiments discussed herein are toprovide examples to enable making or using the subject matter of thisdisclosure, and a person having ordinary skill in the art will readilyunderstand modifications that can be made while remaining withincontemplated scopes of different embodiments. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements. Although method embodiments may be discussed asbeing performed in a particular order, other method embodiments may beperformed in any logical order.

FIGS. 1-9, 10A, 10B, 10C, 11, 12, 13A, and 13B illustrate thecross-sectional views and top views of intermediate stages in theformation of a package including embedded stress absorbers in accordancewith some embodiments of the present disclosure. The correspondingprocesses are also reflected schematically in the process flow shown inFIG. 18 .

FIGS. 1 through 6 illustrate the cross-sectional views in the formationof package component 46 (FIG. 6 ) in accordance with some embodiments ofthe present disclosure. In accordance with some embodiments, packagecomponent 46 is an organic interposer, which includes organic dielectriclayers and redistribution lines formed in the organic dielectric layers.In accordance with other embodiments, package component 46 is asemiconductor interposer, which may include a semiconductor (such assilicon) substrate, through-silicon vias in the semiconductor substrate,and metal lines/vias and/or redistribution lines. In accordance with yetalternative embodiments, package component 46 includes a packagesubstrate, which may be a cored substrate or a coreless substrate.

Referring to FIG. 1 , release film 22 is formed on carrier 20. Therespective process is illustrated as process 202 in the process flow 200as shown in FIG. 18 . Carrier 20 may be a glass carrier, an organiccarrier, or the like. Carrier 20 may have a round top-view shape, andmay have a size of a common silicon wafer. Release film 22 may be formedof a polymer-based material (such as a Light-To-Heat-Conversion (LTHC)material), which may be removed along with carrier 20 from the overlyingstructures that will be formed in subsequent steps. In accordance withsome embodiments of the present disclosure, release film 22 comprises anepoxy-based thermal-release material. Release film 22 may be coated ontocarrier 20.

Dielectric layer 24 is formed on release film 22. The respective processis illustrated as process 204 in the process flow 200 as shown in FIG.18 . In accordance with some embodiments of the present disclosure,dielectric layer 24 is formed of or comprises an organic material suchas a polymer, which may also be a photo-sensitive material such aspolybenzoxazole (PBO), polyimide, benzocyclobutene (BCB), or the like,that may be easily patterned using a photo lithography process. Inaccordance with alternative embodiments, dielectric layer 24 is formedof or comprises an inorganic dielectric material such as silicon oxide,silicon nitride, silicon oxycarbide, silicon oxynitride, silicon oxycarbo-nitride, or the like.

Redistribution Lines (RDLs) 26 are formed over dielectric layer 24. Therespective process is illustrated as process 206 in the process flow 200as shown in FIG. 18 . The formation of RDLs 26 may include forming aseed layer (not shown) over dielectric layer 24, forming a patternedmask (not shown) such as a photo resist over the seed layer, and thenperforming a plating process on the exposed seed layer. The patternedmask and the portions of the seed layer covered by the patterned maskare then removed, leaving RDLs 26 as shown in FIG. 1 . In accordancewith some embodiments of the present disclosure, the seed layer includesa titanium layer and a copper layer over the titanium layer. The seedlayer may be formed using, for example, Physical Vapor Deposition (PVD).The plating process may be performed using, for example, ElectroChemical Plating (ECP), electro-less plating, or the like.

FIGS. 2 through 5 illustrate the formation of a plurality of dielectriclayers and a plurality of RDLs. The respective process is illustrated asprocess 208 in the process flow 200 as shown in FIG. 18 . Referring toFIG. 2 , dielectric layer 28 is formed on RDLs 26. The bottom surface ofdielectric layer 28 is in contact with the top surfaces of RDLs 26 anddielectric layer 24. In accordance with some embodiments of the presentdisclosure, dielectric layer 28 is formed of or comprises a polymer,which may be a photo-sensitive material such as PBO, polyimide, BCB, orthe like. In accordance with alternative embodiments, dielectric layer28 is formed of or comprises an inorganic dielectric material, which maybe selected from the same group of candidate inorganic materials forforming dielectric layer 24. Dielectric layer 28 is then patterned toform openings 30 therein. Hence, some portions of RDLs 26 are exposedthrough the openings 30 in dielectric layer 28.

Further referring to FIG. 3 , RDLs 32 are formed to connect to RDLs 26.RDLs 32 include metal traces (metal lines) over dielectric layer 28.RDLs 32 also include vias extending into the openings in dielectriclayer 28. RDLs 32 are also formed in a plating process, wherein each ofRDLs 32 includes a seed layer (not shown) and a plated metallic materialover the seed layer. The seed layer and the plated material may beformed of the same material or different materials. RDLs 32 may includea metal or a metal alloy including aluminum, copper, tungsten, andalloys thereof.

Referring to FIG. 4 , dielectric layer 34 is formed over RDLs 32 anddielectric layer 28. Dielectric layer 34 may be formed using an organicmaterial such as a polymer, and may be selected from the same candidatematerials as those for forming dielectric layer 28. For example,dielectric layer 34 may be formed of PBO, polyimide, BCB, or the like.Alternatively, dielectric layer 34 may include an inorganic dielectricmaterial such as silicon oxide, silicon nitride, silicon carbide,silicon oxynitride, or the like.

FIG. 5 illustrates the formation of RDLs 36, which are electricallyconnected to RDLs 32. The formation of RDLs 36 may adopt the methods andmaterials similar to that of the underlying RDLs 32 and 26. Next,dielectric layer 38 is formed over RDLs 36. It is appreciated thatalthough in the illustrated example embodiments, three layers of RDLs(26, 32, and 36) are illustrated as an example, the package may have anynumber of RDL layers such as one layer, two layers, or more than threelayers, depending on the routing requirement.

In accordance with some embodiments of the present disclosure,dielectric layer 38 is formed of an organic material such as a polymer,which may further be formed of or comprises PBO, polyimide, BCB, or thelike. In accordance with alternative embodiments, dielectric layer 38 isformed of an inorganic material such as silicon oxide, silicon nitride,silicon carbide, silicon oxynitride, silicon oxy-carbo-nitride, Un-dopedSilicate Glass (USG), or multiplayers thereof.

FIG. 6 illustrates the formation of Under-Bump Metallurgies (UBMs) 42and electrical connectors 44 in accordance with some embodiments. Therespective process is illustrated as process 210 in the process flow 200as shown in FIG. 18 . In order to form UBMs 42, openings are formed indielectric layer 38 to expose the underlying metal pads, which are partsof RDLs 36 in the illustrative example embodiments. In accordance withsome embodiment of the present disclosure, UBMs 42 are formed to extendinto the openings in dielectric layer 38 and to contact the metal padsin dielectric layer 38. UBMs 42 may be formed of nickel, copper,titanium, or multi-layers thereof. In accordance with some exampleembodiments, each of UBMs 42 may include a titanium layer and a copperlayer over the titanium layer.

Electrical connectors 44 are also formed. The formation of electricalconnectors 44 may include placing solder balls on the exposed portionsof UBMs 42, and then reflowing the solder balls, In accordance withthese embodiments, electrical connectors 44 are solder regions. Inaccordance with alternative embodiments of the present disclosure, theformation of electrical connectors 44 includes performing a platingprocess to form solder layers over UBMs 42, and then reflowing thesolder layers. Electrical connectors 44 may also include non-soldermetal pillars, or metal pillars and solder caps over the non-soldermetal pillars, which may also be formed through plating. Throughout thedescription, the structure including release film 22 and the overlyingstructure in combination is referred to as package component 46, whichmay also be referred to as interconnect structure 46. When dielectriclayers 24, 28, 34, and 38 are formed of or comprise an organicmaterial(s) such as a polymer(s), package component 46 is also referredto as an organic interposer.

Referring to FIG. 7 , package components 50A and 50B are bonded topackage component 46. The respective process is illustrated as process212 in the process flow 200 as shown in FIG. 18 . Package components 50Aand 50B are individually and collectively referred to as packagecomponents 50. The bonding may be achieved through solder bonding,metal-to-metal direct bonding, hybrid bonding (including both ofdielectric-to-dielectric bonding and metal-to-metal direct bonding), orthe like. Package components 50A and 50B are individually andcollectively referred to as package components 50 hereinafter. It isappreciated that while one group of package components 50A and 50B isillustrated, there may be a plurality of groups of package components50, which groups are identical to each other, bonded to packagecomponent 46. Examples of the plurality of groups of package components50A and 50B are illustrated in FIGS. 10B and 10C. In addition, eachgroup may be a single-component group including a single packagecomponent 50, or may include a plurality of (such as two, three, ormore) package components 50.

Each of package components 50 may be a device die, a package with adevice die(s) packaged therein, a System-on-Chip (SoC) die including aplurality of device dies packaged as a system, or the like. The devicedies in package components 50 may be or may comprise logic dies, memorydies, input-output dies, Integrated Passive Devices (IPDs), or the like,or combinations thereof. For example, the logic device dies in packagecomponents 50 may be Central Processing Unit (CPU) dies, GraphicProcessing Unit (GPU) dies, mobile application dies, Micro Control Unit(MCU) dies, BaseBand (BB) dies, Application processor (AP) dies, or thelike. The memory dies in package components 50 may include Static RandomAccess Memory (SRAM) dies, Dynamic Random Access Memory (DRAM) dies, orthe like. The device dies in package components 50 may includesemiconductor substrates and interconnect structures, which arerepresented by semiconductor substrate 52 and interconnect structure 54,respectively, in FIG. 7 as an example.

Referring to FIG. 8 , underfill 56 is dispensed. The respective processis illustrated as process 214 in the process flow 200 as shown in FIG.18 . In accordance with some embodiments, underfill 56 includes a basematerial (such as an epoxy) and filler particles in the epoxy, and isflowable. For example, underfill 56 may be dispensed from one side ofpackage components 50, and flows into the gaps between packagecomponents 50 and the underlying package component 46, and into the gapsbetween neighboring package components 50 through capillary.

Referring to FIG. 9 , stress absorbers 58 are dispensed or attached. Therespective process is illustrated as process 216 in the process flow 200as shown in FIG. 18 . In accordance with some embodiments, stressabsorbers 58 are flowable, and are dispensed through a dispenser. Theviscosity of stress absorbers 58 is high, so that after dispensing,stress absorbers 58 may stand by themselves and maintain their shapes,until they are cured into solid. For example, the viscosity of stressabsorbers 58 may be higher than the viscosity of underfill 56. Inaccordance with some embodiments, stress absorbers 58 include a baseflowable material, which may be an epoxy, a resin, a polymer, or thelike. The properties of stress absorbers 58 are discussed in subsequentparagraphs. The base flowable material in stress absorbers 58 may be ahomogeneous material, with the entirety of stress absorbers 58 beingformed of the same material. Some example base materials of stressabsorbers 58 may be selected from an epoxy-based resin, for example,Henkel NCA-3280, Namics XS8345D-47, or a silicone-based adhesive such asShin-Etsu SMC-7030, or the like. These materials have the ability offorming stress absorbers having high aspect ratios and intended shapes.Also, these materials have high moisture resistance. Stress absorbers 58may (or may not) include other materials in the base flowable material.

In accordance with some embodiments, the entirety of stress absorbers 58is formed of a homogeneous material, for example, the flowable basematerial. In accordance with other embodiments, as shown in FIG. 17 ,stress absorbers 58 may include base material 58A and filler particles58B in base material 58A. Filler particles 58B are used for improvingthe overall viscosity value of stress absorbers 58. In accordance withsome embodiments, filler particles 58B are formed of silica, aluminumoxide, rubber, or the like. In accordance with some embodiments, fillerparticles 58B are pre-made solid particles, which are mixed with theflowable base material of filler particles 58B.

In accordance with some embodiments in which stress absorbers 58 areflowable, stress absorbers 58 are dispensed using a dispenser. Thedispensing may be performed using a stencil to define the shape ofstress absorbers 58. Alternatively, stress absorbers 58 are dispensedwithout using any stencil. When dispensed without using stencil, stressabsorbers 58 may have irregular shapes. For example, the sidewalls ofstress absorbers 58 may be non-vertical, for example, being slanted andcurved. The top surfaces of stress absorbers 58 may also be non-planar,for example, stress absorbers 58 may have curved top surfaces, and mayor may not have tips. Dashed lines 59 in FIG. 9 illustrate an example ofthe sidewalls and top surfaces of stress absorbers 58. Furthermore, whendispensed without using a stencil, the shapes of stress absorbers 58 arerandom and irregular, and the shapes of stress absorbers 58 may bedifferent from each other. In accordance with alternative embodiments,stress absorbers 58 are pre-made blocks in a solid form, which areattached to the underlying package component 46, for example, through anadhesive film. The pre-made blocks may also be formed of theaforementioned materials, and when these materials involve flowablematerials, the flowable materials are cured to form the pre-made blocks.

In accordance with some embodiments, underfill 56 and stress absorbers58 are cured after the dispensing of stress absorbers 58. The respectiveprocess is illustrated as process 218 in the process flow 200 as shownin FIG. 18 . Stress absorbers 58 and underfill 56 may be fully curedbefore the subsequent dispensing of encapsulant 60 (FIG. 10A).Alternatively, stress absorbers 58 may be partially cured, which meansstress absorbers 58 become more solid, and their viscosity is increased,but is still not fully solid. For example, when a stencil is used,stress absorbers 58 may be partially cured when they are defined by thestencil, and are fully cured after the stencil is removed. The stressabsorbers 58 that are partially cured may be fully cured in thesubsequent curing process of encapsulant 60 (FIG. 10A). Curing stressabsorbers 58 partially at this stage may reduce the total thermalbudget. In addition, during the curing process, stress absorbers 58 mayshrink, and the partial curing of stress absorbers 58 allows moreshrinking of stress absorbers 58 during the curing of encapsulant 60,which makes stress absorbers 58 less compacted, and may absorb morestress. In accordance with yet alternative embodiments in which stressabsorbers 58 have high-enough viscosity, and will not deform during thesubsequent dispensing of encapsulant 60, stress absorbers 58 may stayuncured until encapsulant is dispensed, and will be cured together withencapsulant 60.

In accordance with some embodiments as shown in FIGS. 8 and 9 ,underfill 56 is dispensed before the dispensing of stress absorbers 58.In accordance with alternative embodiments, underfill 56 is dispensedafter the dispensing of stress absorbers 58.

Referring to FIG. 10A, package components 50 and stress absorbers 58 areencapsulated in encapsulant 60. The respective process is illustrated asprocess 220 in the process flow 200 as shown in FIG. 18 . Encapsulant 60fills the gaps between neighboring package components 50 and stressabsorbers 58. Furthermore, encapsulant 60 extends throughout the entirecarrier 20 to encapsulate the multiple groups of package components 50(as shown in an example top view as shown in FIGS. 10B and 10C) and thecorresponding stress absorbers 58. Encapsulant 60 may be formed of orcomprises a molding compound, a molding underfill, an epoxy, and/or aresin. The top surface of encapsulant 60 is higher than the top ends ofpackage components 50 and stress absorbers 58. In accordance with someembodiments, encapsulant 60 may include a base material 58A (FIG. 17 ),which may be a polymer, a resin, an epoxy, or the like, and fillerparticles 58B in the base material 58A. The filler particles 58B mayinclude dielectric particles of SiO₂, Al₂O₃, silica, or the like, andmay have spherical shapes. Also, the spherical filler particles may havethe same or different diameters.

Next, encapsulant 60 is cured, for example, at a temperature in therange between about 120° C. and about 180° C. The respective process isillustrated as process 222 in the process flow 200 as shown in FIG. 18 .In accordance with some embodiments in which stress absorbers 58 arepartially cured at the time encapsulant is dispensed, stress absorbers58 are also cured fully along with encapsulant 60.

After the full curing of stress absorbers 58, encapsulant 60, andunderfill 56, a planarization process such as a Chemical MechanicalPolish (CMP) process or a mechanical grinding process is performed toplanarize encapsulant 60. After the planarization process, there may bea thin layer of encapsulant 60 covering package components 50. Inaccordance with alternative embodiments, the top surface(s) of one ormore package components 50 in each package component group are exposed.In accordance with some embodiments, after the planarization process,stress absorbers 58 are covered by encapsulant 60, as shown in FIG. 10A.In accordance with alternative embodiments, the portions of encapsulant60 covering stress absorbers 58 are removed by the planarizationprocess. Accordingly, after the planarization process, the top surfacesof stress absorbers 58 are revealed, and dashed lines 62 illustrate thetop portions of corresponding stress absorbers 58. Throughout thedescription, the features formed over release film 22 are collectivelyreferred to as reconstructed wafer 64.

FIGS. 10B and 10C illustrate the top views of some example reconstructedwafers 64. The cross-sectional view shown in FIG. 10A may be obtainedfrom the reference cross-section 10A-10A in FIG. 10B. FIGS. 10B and 10Cillustrate a plurality of packages 64′ in reconstructed wafer 64, whichreconstructed wafer 64 will be singulated in subsequent processes toseparate packages 64′ as discrete packages. Packages 64′ are identicalto each other. Referring to FIG. 10B, in accordance with someembodiments, there are a plurality of stress absorbers 58 dispensedinside each of packages 64′. For example, near each of the corners of apackage 64′, there is one stress absorber 58. In accordance with someembodiments, absorbers 58 are formed close to, but are spaced apartfrom, the corners of the respective package 64′. This means that stressabsorbers 58 are spaced apart from the edges and the correspondingcorners of the respective package 64′ by an outer layer of encapsulant60. Having a layer of encapsulant 60 on the outer sides of stressabsorbers 58 (so that stress absorbers 58 are fully embedded inencapsulant 60) may prevent moisture from using stress absorbers 58 as apath to reach locations close to package components 50. Furthermore,simulation results revealed that the regions with highest stress maybein the regions close to, but not extend to, the corners of packages 64′.For example, FIG. 10B illustrates an example region 66, which is theregion with the highest stress and close to one of the corners ofpackages 64′. Accordingly, by forming stress absorbers 58 in the regionsin which the stress is the highest, smaller stress absorbers 58 may beused, while still can achieve good stress-absorption ability.

In accordance with alternative embodiments, as shown in FIG. 10C, stressabsorbers 58 are formed at the corners of packages 64′, and extend intoneighboring packages 64′. For example, as shown in FIG. 10C, each ofstress absorbers 58 may extend into four neighboring packages 64′. Inthese embodiments, each of stress absorbers 58 may be large enough toextend into the regions with the highest stress. These embodiments maybe adopted when stress absorbers 58 are moisture resistant, and whentheir moisture resistance is equal to or higher than the moistureresistance of encapsulant 60.

FIG. 11 illustrates the formation of bottom-side electrical connectorson the bottom side of reconstructed wafer 64. First, a carrier swap isperformed. The respective process is illustrated as process 224 in theprocess flow 200 as shown in FIG. 18 . In the carrier swap process, thetop surface of the reconstructed wafer 64 as shown in FIG. 10A is firstadhered to carrier 69 through release film 68. Next, carrier 20 (FIG.10A) is detached from reconstructed wafer 64. The detaching process mayinclude projecting a light beam (such as a laser beam) on release film22, and the light beam penetrates through the transparent carrier 20. Inthe embodiments in which the light beam is a laser beam, the laser beamscans through the entire release film 22. As a result of thelight-exposure (such as the laser scanning), release film 22 isdecomposed by the heat of the light beam, and carrier 20 may be liftedoff from release film 22. The corresponding process is also referred toas the de-bonding of reconstructed wafer 64 from carrier 20. Theresulting structure is shown in FIG. 11 .

As a result of the de-bonding process, dielectric layer 24 is revealed.Next, UBMs (or metal pads) 70 and electrical connectors 72 are formed.The respective process is illustrated as process 226 in the process flow200 as shown in FIG. 18 . The formation process may include patterningdielectric layer 24 to reveal the conductive pads in RDLs 26, andforming UBMs/pads 70, which extend into the openings in dielectric layer24. UBMs/pads 70 may be formed of or comprise nickel, copper, titanium,or multi-layers thereof. In accordance with some example embodiments,each of UBMs/pads 70 includes a titanium layer and a copper layer overthe titanium layer.

Electrical connectors 72 are then formed. The formation of electricalconnectors 72 may include placing solder balls on the exposed portionsof UBMs/pads 70, and then reflowing the solder balls, and henceelectrical connectors 72 are solder regions. In accordance withalternative embodiments of the present disclosure, the formation ofelectrical connectors 72 includes performing a plating process to formsolder layers over UBMs/pads 70, and then reflowing the solder layers.Electrical connectors 72 may also include non-solder metal pillars, ormetal pillars and solder caps over the non-solder metal pillars, whichmay also be formed through plating.

Next, reconstructed wafer 64 is demounted from carrier 69, for example,by projecting a laser beam on release film 68, so that release film 68is decomposed. The respective process is illustrated as process 228 inthe process flow 200 as shown in FIG. 18 . Referring to FIG. 12 ,reconstructed wafer 64 is placed on tape 74, which is supported by frame76. Reconstructed wafer 64 is then singulated along scribe lines 78, sothat reconstructed wafer 64 is separated into discrete packages 64′. Therespective process is illustrated as process 230 in the process flow 200as shown in FIG. 18 . Package component (interconnect structure) 46 isalso singulated into discrete package component (interconnectstructures) 46′.

Next, as shown in FIG. 13A, package 64′ is bonded with package component82, for example, through electrical connectors 72, which may includesolder regions. The respective process is illustrated as process 232 inthe process flow 200 as shown in FIG. 18 . In accordance with someembodiments, package component 82 may be or may comprise an interposer,a package, a package substrate, a printed circuit board, or the like.Package component 82 includes electrical connectors 84, which may besolder regions. Underfill 86 may be dispensed into the gap betweenpackage 64′ and package component 82. Package 88 is thus formed.

In accordance with some embodiments, the Young's modulus of stressabsorbers 58 is lower than the Young's modulus of encapsulant 60, whichmeans stress absorbers 58 are softer than encapsulant 60. For example,the Young's modulus of stress absorbers 58 may be smaller than about 10GPa, and the Young's modulus of encapsulant 60 may be in the rangebetween about 12 GPa and about 25 GPa. Accordingly, when there is stressin encapsulant 60, which stress is generated due to the differencebetween the Coefficient of Thermal Expansion (CTE) values of packagecomponents 50, package component 46′, and package component 82, stressabsorbers 58 may absorb the stress, and hence the cracking ofencapsulant 60 and the delamination between encapsulant 60 and packagecomponent 46′ are reduced. Furthermore, the difference (YM60−YM58)between the Young's modulus YM60 of encapsulant 60 and the Young'smodulus YM58 of stress absorbers 58 may be greater than about 1 GPa,greater than about 2 GPa, or in the range between about 5 GPa and about10 GPa. Furthermore, ratio (YM60−YM58)/YM60 may be greater than about0.05, greater than about 0.1, greater than about 0.2, and may be in therange between about 0.05 and about 0.5. When stress absorbers 58 includethe base material (such as an epoxy) and fillers, the Young's modulus ofthe fillers 58B (FIG. 17 ) may be smaller than the Young's modulus ofthe base material 58A, so that the filler particles 58B have thefunction of providing more stress-absorption ability. In accordance withalternative embodiments, the Young's modulus of the fillers 58B may beequal to or higher than the Young's modulus of the base material 58A.The filler size and the filler density in stress absorbers 58 may besmaller than the corresponding filler size and the filler density,respectively, in encapsulant 60.

The CTE value CTE₅₈ of stress absorbers 58 may be equal to the CTE valueCTE₆₀ of encapsulant 60, so that during thermal cycles, stress absorbers58 will not delaminate from encapsulant 60, and there is no additionalstress generated due to the difference between the CTE values of stressabsorbers 58 and encapsulant 60. Alternatively, The CTE value CTE₅₈ ofstress absorbers 58 is slightly different from, and is substantiallyequal to, the CTE value CTE₆₀ of encapsulant 60, for example, with theabsolute value of (CTE₅₈−CTE₆₀)/CTE₆₀ being smaller than about 0.3,smaller than about 0.2, or smaller than about 0.1.

FIG. 13B illustrates a top view of package 88 in accordance with someembodiments. In the illustrated example embodiments, underfill 56 isspaced apart from the edges of package 64′ by spacings L1 and W1. Inaccordance with some embodiments, stress absorbers 58 have length L2 andwidth W2, with length L2 being smaller than or equal to length L1, andwidth W2 being smaller than or equal to width W1, so that stressabsorbers 58 may be placed on package component 46′ without standing onunderfill 56. Furthermore, as shown in FIG. 13A, the height H2 of stressabsorbers 58 may be smaller than or equal to (as represented by dashedlines 62) the height H1 of encapsulant 60. For example, when stressabsorbers 58 is formed of or comprise a material that is prone tomoisture penetration, H2 is smaller than H1. Otherwise, height H2 isequal to height H1. Furthermore, the difference (H1-H2) may be greaterthan about 50 μm, so that the portions of encapsulant 60 on top ofstress absorbers 58 may adequately prevent moisture from reaching stressabsorbers 58. Otherwise, the moisture that reaches stress absorbers 58may use stress absorbers 58 as paths to get closer to device dies 50.

FIG. 14A illustrates package 88 in accordance with alternativeembodiments. The package 88 shown in FIG. 14A is similar to the package88 in FIG. 13 , except that stress absorbers 58 extend to the edges ofpackages 64′. The embodiments in FIG. 14A may be formed by adopting thereconstructed wafer 64 in FIG. 10C, so that when reconstructed wafer 64is singulated, each of stress absorbers 58 may be separated intoneighboring discrete packages 64′.

FIG. 14B illustrates a top view of the package 88 as shown in FIG. 14A.Stress absorbers 58 extend to the corresponding edges and thecorresponding corners of package 64′. Each of stress absorbers 58 mayinclude two edges, which are also parts of the edges of package 64′.

FIG. 15 illustrates a top view of package 88 in accordance withalternative embodiments. The cross-sectional view of the correspondingpackage 88 may also be found referring to FIG. 13A. As shown in FIG. 15, stress absorbers 58 may be aligned to a ring, which includes cornerportions close to the corresponding corners of package 64′, and edgeportions close to and parallel to the corresponding edges of package64′. In accordance with some embodiments, stress absorber 58 forms afull ring, with no break therein. In accordance with some embodiments,stress absorbers 58 include a plurality of pieces aligned to the ring,but the plurality of pieces are separated from each other. For example,the regions 90 as marked by dashed rectangles may be free from stressabsorbers 58 therein.

FIG. 16 illustrates a top view of package 88 in accordance withalternative embodiments. The cross-sectional view of the correspondingpackage 88 may also be found referring to FIG. 13A. The embodiment shownin FIG. 16 is similar to the embodiments shown in FIG. 15 , except thatinside the stress absorber ring, there are stress absorber extensions58′. Forming stress absorber extensions 58′ may enlarge stress absorberextensions 58′ in the corner regions, where stress is the highest.Similar to FIG. 15 , in the package 88 as shown in FIG. 16 , stressabsorbers 58 may be aligned to a ring including corner portions close tothe corresponding corners of package 64′, and edge portions close to andparallel to the corresponding edges of package 64′. In accordance withsome embodiments, stress absorber 58 forms a full ring, with no breaktherein. In accordance with some embodiments, stress absorbers 58include a plurality of pieces aligned to the ring, but the plurality ofpieces are separated from each other. For example, the regions 90 asmarked by dashed rectangles may be free from stress absorbers 58therein.

FIG. 17 illustrates a magnified view of a portion of example stressabsorber 58 and encapsulant 60 in region 92 in FIG. 13A (or FIG. 14A).In accordance with some embodiments, stress absorber 58 includes basematerial 58A and filler particles 58B in base material 58A. Inaccordance with alternative embodiments, the material of the entirestress absorber 58 is homogeneous, and no filler particles are included.Accordingly, filler particles 58B are shown as being dashed to indicatethey may or may not be formed. Encapsulant may include base material 60Aand filler particles 60B in base material 60A. As aforementioned, stressabsorber 58 is softer (with smaller Young's modulus) than encapsulant60. Filler particles 58B may also have a Young's modulus smaller than,equal to, or greater than, the Young's modulus of filler particles 60B.

Experiment results have demonstrated that with the formation of stressabsorbers 58, the stress in package 88 is reduced when stress absorbers58 are placed in selected positions. For example, the experiment resultsindicated that when the stress absorbers 58 are placed to the positionsas shown in FIG. 13B, the stress may be reduced by about 28 percent toabout 62 percent, depending on the material and the size of stressabsorbers 58. On the other hand, if the stress absorbers 58 are placed,but do not include portions at corners, the stress may increase, ratherthan decrease. For example, experiment results indicated that if thestress absorbers 58 are placed in regions 94 in FIG. 14B only, thestress may increase by about 34 percent to about 71 percent. Thisindicates that besides the material of stress absorbers 58, thelocations of stress absorbers 58 also affect the results. For example,the stress absorbers 58 having lengthwise direction and width directionparallel to the lengthwise directions and width directions (for example,X-directions and Y-directions as in FIG. 14B), respectively, of therectangle encircling the package components 50 (and do not overlap withpackage components 50) has better effect in reducing stress than stressabsorbers overlapping package components 50.

The embodiments of the present disclosure have some advantageousfeatures. By selecting proper materials for stress absorbers 58, andforming stress absorbers 58 at proper locations of packages, the stressin the packages may be reduced. The delamination and cracking ofencapsulant are also reduced.

In accordance with some embodiments of the present disclosure, a methodincludes bonding a first package component over a second packagecomponent, wherein the second package component comprises a plurality ofdielectric layers; and a plurality of redistribution lines in theplurality of dielectric layers; dispensing a stress absorber on thesecond package component; curing the stress absorber; and forming anencapsulant on the second package component and the stress absorber. Inan embodiment, the stress absorber has a first Young's modulus lowerthan a second Young's modulus of the encapsulant. In an embodiment, thedispensing the stress absorber comprises dispensing a homogeneousmaterial. In an embodiment, the dispensing the stress absorber comprisesdispensing a mixed material with a base material and filler particlesmixed in the base material. In an embodiment, the filler particles havea first Young's modulus smaller than a second Young's modulus of thebase material. In an embodiment, the method further includes performinga singulation process to separate the second package component into adiscrete package, wherein in the discrete package, the stress absorberis spaced apart from corresponding nearest edges and nearest corners ofthe discrete package. In an embodiment, the method further includesperforming a singulation process to separate the second packagecomponent into a discrete package, wherein the stress absorber is sawedapart in the singulation process. In an embodiment, the method furtherincludes performing a planarization process on the encapsulant, whereinafter the planarization process, the stress absorber is covered by aportion of the encapsulant. In an embodiment, the method furtherincludes dispensing an underfill between the first package component andthe second package component, wherein the underfill and the stressabsorber are cured in a same curing process.

In accordance with some embodiments of the present disclosure, a packageincludes an interconnect structure comprising a plurality of dielectriclayers; and a plurality of redistribution lines in the plurality ofdielectric layers; a package component over the interconnect structure,wherein the package component comprises a device die; a stress absorberover the interconnect structure, wherein the stress absorber has a firstYoung's modulus; and an encapsulant on the package component and thestress absorber, wherein the encapsulant has a second Young's modulusgreater than the first Young's modulus. In an embodiment, the stressabsorber is in physical contact with the encapsulant. In an embodiment,the stress absorber has a non-vertical and non-straight sidewalls andnon-planar top surface. In an embodiment, the stress absorber comprisesa base material selected from an epoxy, a resin, or combinationsthereof. In an embodiment, the stress absorber further comprises fillerparticles in the base material. In an embodiment, an entirety of thestress absorber is formed of a homogeneous material.

In accordance with some embodiments of the present disclosure, a packageincludes a first package component comprising an interconnect structure,which comprises a plurality of dielectric layers; and a plurality ofredistribution lines in the plurality of dielectric layers; a secondpackage component over and bonded to the interconnect structure, whereinthe second package component comprises a device die; a plurality ofstress absorbers over the interconnect structure, wherein the pluralityof stress absorbers comprise a corner stress absorber close to a cornerof the interconnect structure, and wherein the plurality of stressabsorbers comprise a first organic material; and an encapsulantphysically contacting at least sidewalls of the corner stress absorber,wherein the encapsulant comprises a second organic material differentfrom the first organic material. In an embodiment, the plurality ofstress absorbers have a first Young's modulus, and the encapsulant has asecond Young's modulus, and wherein the first Young's modulus is smallerthan the second Young's modulus. In an embodiment, the corner stressabsorber is spaced apart from edges of the first package component. Inan embodiment, the corner stress absorber extends to the corner of thefirst package component. In an embodiment, the package further includesa third package component underlying and bonding to the first packagecomponent.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: bonding a first packagecomponent over a second package component, wherein the second packagecomponent comprises: a plurality of dielectric layers; and a pluralityof redistribution lines in the plurality of dielectric layers;dispensing a stress absorber on the second package component; curing thestress absorber; and forming an encapsulant on the second packagecomponent and the stress absorber, wherein the stress absorber has afirst Young's modulus lower than a second Young's modulus of theencapsulant.
 2. The method of claim 1, wherein the dispensing the stressabsorber comprises dispensing a homogeneous material.
 3. The method ofclaim 1, wherein the dispensing the stress absorber comprises dispensinga mixed material with a base material and filler particles mixed in thebase material.
 4. The method of claim 3, wherein the filler particleshave a third Young's modulus smaller than a fourth Young's modulus ofthe base material.
 5. The method of claim 1 further comprisingperforming a singulation process to separate the second packagecomponent into a discrete package, wherein in the discrete package, thestress absorber is spaced apart from corresponding nearest edges andnearest corners of the discrete package.
 6. The method of claim 1further comprising performing a singulation process to separate thesecond package component into a discrete package, wherein the stressabsorber is sawed apart in the singulation process.
 7. The method ofclaim 1 further comprising performing a planarization process on theencapsulant, wherein after the planarization process, the stressabsorber is covered by a portion of the encapsulant.
 8. The method ofclaim 1 further comprising dispensing an underfill between the firstpackage component and the second package component, wherein theunderfill and the stress absorber are cured in a same curing process. 9.A method comprising: forming an interconnect structure comprising: aplurality of dielectric layers; and a plurality of redistribution linesin the plurality of dielectric layers; bonding a package component overthe interconnect structure, wherein the package component comprises adevice die; forming a stress absorber over the interconnect structure,wherein the stress absorber has a first Young's modulus; andencapsulating the package component and the stress absorber in anencapsulant, wherein the encapsulant has a second Young's modulusgreater than the first Young's modulus.
 10. The method of claim 9,wherein the stress absorber is in physical contact with the encapsulant.11. The method of claim 9, wherein the stress absorber has anon-vertical and non-straight sidewalls and non-planar top surface. 12.The method of claim 9, wherein the stress absorber comprises a basematerial selected from an epoxy, a resin, or combinations thereof. 13.The method of claim 12, wherein the stress absorber further comprisesfiller particles in the base material.
 14. The method of claim 9,wherein an entirety of the stress absorber is formed of a homogeneousmaterial.
 15. A method comprising: forming a first package componentcomprising: an interconnect structure comprising: a plurality ofdielectric layers; and a plurality of redistribution lines in theplurality of dielectric layers; bonding a second package component overthe interconnect structure; dispensing a plurality of stress absorbersover the interconnect structure, wherein the plurality of stressabsorbers comprise a corner stress absorber close to a corner of theinterconnect structure; dispensing an molding compound physicallycontacting at least sidewalls of the corner stress absorber, whereineach of the plurality of stress absorbers and the molding compoundcomprises a base material and filler particles in the base material; andperforming curing processes to solidify the plurality of stressabsorbers and the molding compound.
 16. The method of claim 15, whereinthe curing processes comprise: a first curing process to partially curethe plurality of stress absorbers; and a second curing process to fullycure the plurality of stress absorbers that have been partially curedand the molding compound.
 17. The method of claim 15 further comprisingplanarizing the molding compound, wherein after the planarizing, topsurfaces of the plurality of stress absorbers are lower than a topsurface of the molding compound.
 18. The method of claim 15 furthercomprising sawing through the molding compound and the first packagecomponent into a package, wherein after the sawing, the plurality ofstress absorbers are spaced apart from edges of the package.
 19. Themethod of claim 15 further comprising sawing through the moldingcompound and the first package component into a package, wherein in thesawing, one of the plurality of stress absorbers is sawed.
 20. Themethod of claim 15, wherein the plurality of stress absorbers have afirst Young's modulus lower than a second Young's modulus of the moldingcompound.